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Astrophysics > High Energy Astrophysical Phenomena

Title:Magnetars: a short review and some sparse considerations

Abstract: We currently know about 30 magnetars: seemingly isolated neutron stars whose
properties can be (in part) comprehended only acknowledging that they are
endowed with magnetic fields of complex morphology and exceptional intensity-at
least in some components of the field structure. Although magnetars represent
only a small percentage of the known isolated neutron stars, there are almost
certainly many more of them, since most magnetars were discovered in transitory
phases called outbursts, during which they are particularly noticeable. In
outburst, in fact, a magnetar can be brighter in X-rays by orders of magnitude
and usually emit powerful bursts of hard-X/soft-gamma-ray photons that can be
detected almost everywhere in the Galaxy with all-sky monitors such as those on
board the Fermi satellite or the Neil Gehrels Swift Observatory. Magnetars
command great attention because the large progress that has been made in their
understanding is proving fundamental to fathom the whole population of isolated
neutron stars, and because, due to their extreme properties, they are relevant
for a vast range of different astrophysical topics, from the study of gamma-ray
bursts and superluminous supernovae, to ultraluminous X-ray sources, fast radio
bursts, and even to sources of gravitational waves. Several excellent reviews
with different focuses were published on magnetars in the last few years: among
others, Israel and Dall'Osso (2011); Rea and Esposito (2011); Turolla and
Esposito (2013); Mereghetti et al. (2015); Turolla et al. (2015); Kaspi and
Beloborodov (2017). Here, we quickly recall the history of these sources and
travel through the main observational facts, trying to touch some recent and
sometimes little-discussed ramifications of magnetars.